Internet protocol telephone system

ABSTRACT

An internet protocol telephone includes a substrate having an input and an output that are capable of being connected to the internet protocol (IP) network. A relay is disposed on the substrate and is connected between the input and the output of the substrate. The relay includes first and second native FETs that have a threshold voltage of approximately zero volts. Therefore, the relay is nominally turned-on, even when little or no voltage (or power) is applied to the IP telephone substrate, as during the discovery mode of IP telephone operation. During discovery mode, The IP phone is configured to be responsive to extended link pulses and block data packets that are associated with legacy devices. Data packets have a higher signal duration and are more continuous than extended link pulses. The IP phone includes a switchable ground that is connected to the gates of the native devices, and is controlled by a rectifier and filter circuit that are connected to the substrate input. If the IP phone receives legacy data packets during discovery mode, then the high signal duration and continuous nature of the data packets are sufficient to cause the rectifier to generate a rectified signal having sufficient amplitude to activate the switchable ground, so as to ground the gates of the native devices and therefore turn-off the native devices. Therefore, the data packets are rejected and are not passed back to the switch. Extended link pulses have a frequency that is too low to generate a rectified signal that is sufficient to activate the switchable ground, and therefore the native devices remain turned-on. Accordingly, the extended link pulses are passed back to the switch.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/673,809, filed on Apr. 22, 2005, which is incorporated herein byreference in its entirety; and

This application is also a continuation-in-part of application Ser. No.10/028,781, filed on Dec. 28, 2001, which claims the benefit of U.S.Provisional Application No. 60/258,777, filed on Dec. 28, 2000, both ofwhich are incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a communications device. Morespecifically, the present invention is related to an Internet Protocol(IP) telephone having an on-chip native device relay, and an on-chiprectifier and filter for controlling the native device relay duringdiscovery and normal operation modes.

2. Background Art

In addition to data communications, the Internet can also be used tocarry voice telephony. One conventional system that carries voicecommunications over the Internet utilizes an Internet Protocol (IP), andsuch telephones are referred to as IP telephones.

The data terminal equipment (DTE) of an IP telephone includes atelephone line that is connected to a computer device through aseries-connected relay (i.e. switch). The relay switches an incomingtelephone signal to either the computer or to a filter that is connectedin parallel with the computer. The filter is connected/disconnectedacross the computer depending on the state of the IP phone system byclosing/opening the associated relay. In a no power or “discovery” mode,the relay is switched so the filter is connected across a physical layerinput of the computer. Therefore, the filter receives an incoming signalon the telephone line (or cable, e.g. CAT-5) and returns low frequencysignals back down the telephone line, without the incoming signalreaching the physical layer of the computer. The reflected low frequencysignals indicate that a compatible IP phone is available for use.Specifically, during this auto-negotiation, the low frequency signalthat is sent to identify IP phones (and other compatible devices) isreferred to as an “extended link pulse”. In contrast, legacy switchessend normal link pulses to identify legacy devices prior to data packettransmission.

When power is applied to the relay in a “normal operation” mode, therelay is switched so the filter is disconnected from the input of thephysical layer of the computer. Therefore, the filter does not effectthe incoming signal, and the incoming signal is applied to the physicallayer of the computer for further processing.

The continual opening and closing of the relay creates wear and tear ofthe relay components as the conventional IP phone switches between thediscovery and normal modes, eventually causing component failure. Itwould be more cost-effective to keep the filter connected at all times,thereby eliminating relay replacement. Additionally, the conventionalrelay is not integrated with the computer or the filter, which increasesthe manufacturing part count and ultimately the manufacturing cost of anIP Phone.

The conventional IP telephone also includes a signal termination circuitthat provides a good input impedance for the incoming signal when thefilter is not connected across the computer. Proper signal terminationis necessary to provide a good signal match, which aids in proper signalreception during the normal operation mode. The termination circuit is aseparate off-chip device, which increases the manufacturing part countand ultimately the manufacturing cost of an IP Phone. It is desirable tointegrate the termination circuit in order to reduce the part countduring the manufacturing process.

The filter in the conventional IP telephone is a conventional lowpassfilter. The conventional lowpass filter has an input impedance that ishighly dependent on the frequency of the input signal that is deliveredto the filter. Input frequencies that are outside of the filter passbandare substantially reflected, which can produce an undesired high returnloss. Also, conventional filters are highly sensitive to variations inthe filter components and in the variation of components that areconnected to the filter.

An additional problem can occur when an IP phone is connected to aswitch via relatively short cable. Specifically, if a legacy switchsends normal link pulses over the LAN to an IP telephone, the normallink pulses can pass through the filter without sufficient attenuationduring discovery mode, thereby causing the legacy switch to think the IPphone is a legacy device. In other words, the devices will link up. Ifthe legacy switch then transmits data packets over the LAN, then thesedata packets can also pass through the filter, creating an unintendedsignal loop that violates IEEE standards.

What is needed is a filter that has a constant impedance for allfrequencies, even frequencies that are outside the passband of thefilter. Furthermore, the filter should be relatively insensitive tocomponent variation.

Further, it would also be desirable to an IP phone that can distinguishbetween data packets and extended link pulses for short cable lengthapplications, and prevent the re-transmission of data packets duringdiscovery mode to as to prevent unauthorized signal loop transmissions.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a communication device that is capableof being connected to a communications network. The communicationsdevice can be, for example, an internet protocol (IP) telephone that isconnected to an IP telephone network. Alternatively, the communicationsdevice can a wireless access point, a laptop computer, or a localswitch.

The communications device includes a physical layer having a substratewith an input and an output that are capable of being connected to theinternet protocol (IP) network. A relay is disposed on the substrate andis connected between the input and the output of the substrate. Therelay includes first and second native FETs that have a thresholdvoltage of approximately zero volts. Therefore, the relay is nominallyturned-on, even when little or no voltage (or power) is applied to thephysical layer substrate, as during the discovery mode of IP telephoneoperation.

During discovery mode, the communications device is configured to beresponsive to extended link pulses and block data packets that areassociated with legacy devices. Data packets have a higher signalduration than extended link pulses. In other words, data packets aremore continuous than extended link pulses so as to have more energy onthe cable for a much longer period of time than extended link pulses.For example, data packets can be signal bursts that last as long as 1-3microseconds. The communications device recognizes the difference insignal duration between the data packets and the extended link pulses,and opens the relay for data packets.

The communications device (e.g. IP phone) includes a switchable groundthat is connected to the gates of the native devices. The switchableground is controlled by a rectifier and filter circuit that areconnected to the substrate input. If the communications device receivesdata packets during discovery mode, then the continuous nature of thedata packets will cause the rectifier to generate a rectified signalwith sufficient amplitude to activate the switchable ground. The outputof the rectifier is low pass filtered. As a result, the rectifier outputgrounds the gates of the native devices and therefore turns-off thenative devices after some delay of receiving the data packets.Therefore, the data packets are rejected and are not passed back to theIP switch. Extended link pulses have a signal duration that is too lowto generate a rectified signal that is sufficient to activate theswitchable ground. Therefore, the native devices remain turned-on.Accordingly, the extended link pulses are passed back to the IP switch.

During normal operation, additional rectifier circuits rectify an inputsignal received at an input of the filter, to produce a rectified signalthat is applied to the gates of the first and second native FETs, so asto further improve the conductivity of the relay.

Further features and advantages of the invention, as well as structureand operation of various embodiments of the invention, are disclosed indetail below will reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

The present invention is described with reference to the accompanyingdrawings. In the drawings, like reference numbers indicate identical orfunctionally similar elements. Additionally, the left-most digit(s) of areference number identifies the drawing in which the reference numberfirst appears.

FIG. 1 a illustrates a conventional IP telephone, wherein a filter isplaced between two relays, and termination resistors are placed outsidea computer chip.

FIG. 1 b illustrates a block diagram of a conventional IP telephone indiscovery mode.

FIG. 1 c illustrates a conventional IP telephone in normal operationmode.

FIG. 2 a illustrates an IP telephone having a filter continuallyconnected to the computer at all times, according to embodiments of thepresent invention.

FIG. 2 b illustrates a block diagram of an IP telephone according to thepresent invention.

FIG. 2 c is another embodiment of a present invention IP telephonesystem.

FIG. 2 d illustrates a block diagram of an IP telephone in discoverymode, according to embodiments of the present invention.

FIG. 2 e illustrates a block diagram of an IP telephone in normaloperation mode, according to embodiments of the present invention.

FIG. 3 a. illustrates a conventional low pass RL filter.

FIG. 3 b illustrates a conventional low pass RC filter.

FIG. 3 c illustrates a low pass and a high pass filter.

FIG. 3 d illustrates a conventional Butterworth filter.

FIG. 4 a illustrates a block diagram of the filter functions in thepresent invention.

FIG. 4 b illustrates a multi-pole constant impedance low pass filter,according to embodiments of the present invention.

FIG. 4 c illustrates a multi-pole constant impedance bandpass filter,according to embodiments of the present invention.

FIG. 4 d illustrates a multi-pole constant impedance differential lowpass filter, according to embodiments of the present invention.

FIG. 4 e illustrates a second multi-pole constant impedance differentiallow pass filter, according to embodiments of the present invention.

FIG. 5 a further illustrates a present invention relay.

FIG. 5 b illustrates another embodiment of the relay in the presentinvention.

FIG. 5 c illustrates another embodiment of the relay in the presentinvention.

FIG. 5 d illustrates yet another embodiment of the relay in the presentinvention.

FIG. 5 e illustrates yet another embodiment of the relay in the presentinvention.

FIG. 6 illustrates a communications system having power provided over aLAN to an IP phone.

FIG. 7 illustrates a discovery mode of a communications system havingnormal link pulses and extended link pulses, and a filter coupled acrossthe substrate terminals.

FIG. 8A illustrates further illustrates a discovery mode of acommunications system and having a filter coupled to the filter input ofthe physical layer device.

FIG. 8B further defines the extended link pulses 701.

FIG. 8C illustrates data packets in a LAN environment.

FIG. 9 further illustrates a physical layer device during discoverymode.

FIG. 10 further illustrates the physical layer device.

FIG. 11 further illustrates a physical layer device according toembodiments of the present invention, where a rectifier is used toturn-off the native relay devices for data packets during discoverymode.

DETAILED DESCRIPTION OF THE INVENTION

Conventional Internet Protocol Telephone

FIG. 1 a illustrates a conventional IP telephone system 125 having adata network 110 and a conventional IP telephone 100. The data network110 can be the publically available Internet, or another type of publicor private network. The IP telephone 100 receives signals 102 from thenetwork 110 at an input terminal 105, and transmits signals 103 to thedata network 110 at the output terminal 106. In embodiments, the signals102 and 103 carry voice communications using Internet Protocol.

The IP telephone 100 includes a filter 104, relays 120 and 121, and aphysical layer 101 that is part of a computer chip (not shown) or othertype of integrated circuit. The computer chip processes voice and datasignals that are sent to and received from the data network 110. Therelay 120 connects the input terminal 105 to either the filter 104 or aninput terminal 108 of the physical layer 101. Likewise, the relay 121connects the output terminal 106 to either the filter 104 or an output109 of the physical layer 101. The relays 120 and 121 are nominallyconnected to the filter 104 when no power is applied to the relays.(i.e., discovery mode) When power is applied, the relays 120 and 121switch and connect the terminals 105 and 106 to the respective terminals108 and 109 of the physical layer 101 (i.e., normal operation mode).Grounded termination resistors 122 and 123 are inserted between thefilter 104 and physical layer 101 to provide a good match and preventunwanted signal reflections from affecting the input and output signals102 and 103.

FIG. 1 b further describes the operation of the IP phone in discoverymode, where no power is applied to either the relays 120, 121, or thephysical layer 101. During discovery mode (FIG. 1 b), the relay 120connects the input terminal 105 to the input of the filter 104, and therelay 121 connects the output of the filter 104 to the output terminal106. Therefore, the input signal 102 is filtered by the filter 104 andthe filtered output is re-transmitted to data network 110 as thetransmit signal 103. The filter 104 is configured as a lowpass filterwith a pre-determined cutoff frequency that is compatible with the datanetwork 110. In discovery mode, the data network 110 analyzes thetransmit signal 103 for the correct low frequency components todetermine that the IP phone 100 is compatible for future communication.

FIG. 1 c further describes the operation of the IP phone 100 in normaloperation mode, where power is applied to the relays 120, 121, and thephysical layer 101. During normal operation (FIG. 1 c), the relay 120switches the input terminal 105 from the filter 104 to the physicallayer input 108. Likewise, the relay 121 switches the output terminal106 from the filter 104 to the output 109 of the physical layer 101.Therefore the physical layer input 108 is connected to the receiveterminal 105, and the physical layer output 109 is connected to theoutput terminal 106 so that communication with the network 110 cancommence. The resistor 122 should be highly accurate as the impedance ofthis resistor circuit must be matched with the impedance of the physicallayer to prevent signal mismatch.

The IP phone 100 is relatively expensive to implement because the relaymechanisms 120 and 121, and the termination resistors 122 and 123 arelocated outside the physical layer 101, resulting in increased assemblycost.

IP Phone System with On-Chip Relay and Constant Impedance Filter

FIG. 2 a illustrates IP telephone 200 according to embodiments of thepresent invention. IP telephone 200 has on-chip relays and a constantimpedance filter according to embodiments of the present invention. TheIP telephone 200 receives signals 201 from the network 110 at an inputterminal 202, and transmits signals 214 to the network 110 at an outputterminal 213.

IP telephone 200 includes a first termination resistor 212, a filter204, and a physical layer 208 that is part of a computer chip (notshown), or other IC. The physical layer 208 can be implemented on asemiconductor substrate, for example and CMOS substrate. The physicallayer 208 includes a second termination resistor 206, a switch 205, anda relay 210 that are all located on the physical layer 208, which isdistinct from the conventional IP phone 100 that has the relays and bothtermination resistors located off-chip. Furthermore, the filter 204 ispermanently connected to an input terminal 202 of the IP phone 200.Therefore, the filter 204 is not switched in and out of the receivepath, as in the conventional IP phone 100.

The relay 210 includes a native MOSFET device, which has a thresholdvoltage that is equal to substantially zero volts. Therefore, the relay210 conducts even when no voltage is applied to the gate of relay 210.Whereas, the switch 205 is conventional MOSFET device that requires anon-zero voltage source to close the switch 205. The properties of therelay 210 and native devices are further described herein.

FIG. 2 d further describes the operation of the IP phone 200 indiscovery mode, where no power is applied to the physical layer 208.

During discovery mode, the filter 204 receives the input signal 201 andgenerates a filtered output signal 215 that is applied to the physicallayer 208 at terminal 209. The relay 210 is closed during discovery modeso that the filtered output signal 215 is transmitted to the datanetwork 110 as the output signal 214. The filter 204 is configured as alowpass filter with a pre-determined cutoff frequency that is compatiblewith the data network 110. In discovery mode, the data network 110analyzes the transmit signal 214 for the correct low frequencycomponents to determine that the IP phone 200 is compatible for futurecommunication. The input signal 201 is also received at the physicallayer input terminal 203. However, no power is applied to the physicallayer 208 during discovery mode, so the A/D 250 and receiver 251 are notpowered up. Therefore, the input signal 201 is not further processed bythe physical layer 208 during discovery mode.

FIG. 2 e further describes the operation of the IP phone 200 in normaloperation mode, where power is applied to the physical layer 208. Duringnormal operation, power is applied to the physical layer 208, whichopens the relay 210 and closes the switch 205. By opening the relay 210,the filter output 215 is not re-transmitted to the data network 110.However, the physical layer 208 is powered-up so that the input signal201 is received at the physical layer 208. There is no need for an extratermination resistor located off-chip, such as termination resistor 122of FIG. 1 c, because the impedance of the filter 204 and the terminationresistor 206 matches the input impedance. As will be described laterwith respect to the filter 204, the filter 204 is insensitive tocomponent variation. Therefore, the termination resistor 206 can beplaced on-chip and does not affect filter 204 frequency response orimpedance of the filter 204. The filter 204 and the termination resistor206 serve to properly terminate the signal on-chip. Furthermore, theanalog-to-digital converter 250 and the receiver 251 further process thesignal 201. More specifically, the analog to digital converter 250samples and encodes the analog signal to create a digital signal. Theprocess may be accomplished by a digital signal processor (DSP). Thereceiver 251 is a device that receives a transmission signal. Thereceiver 251 may also be described as a portion of a telecommunicationsdevices that decodes an encoded signal into a desired for. For example,the receiver 251 process the digital signal from the analog to digitalconverter 250 to extract useful information from the data network 110.Furthermore, the physical layer output terminal 211 is still directlyconnected to the output terminal 213. Therefore, normal communicationsare carried-on with the network 110 through the input terminal 202 andoutput terminal 213.

A high-level diagram of the constant impedance filter 204 is shown inFIG. 4 a. The filter 204 accepts the input signal 201 and selects a bandof frequencies in the filter output 215 that are passed to the input 209of the physical layer 208. Furthermore, the filter 204 terminates anyundesired frequencies 492 that are not passed to the output 212. Thefilter 204 is described further in following sections.

Other embodiments of the Internet Protocol system are possible, however,the above is a description of one embodiment and not to be construed aslimiting the scope of the present invention, except as designated by theclaims that follow.

Relay

FIG. 2 b further illustrates the physical layer 208 that has the relay210 and the termination resistor 206. The physical layer 208 isillustrated in a differential implementation, as compared to asingle-ended implementation. The termination resistor 206 is connectedto the output of the filter 204 via input terminals 233, 234, whereterminals 233, 234 represent a differential input for input 216. Thetermination resistor 206 is implemented with resistors 271, 272, andPMOSFET 273. The relay 210 is connected to the output of the terminationresistor 206, and is implemented with output native devices 235 and 236.The output native devices 235 and 236 are connected to respective outputterminals 237 and 238, where terminals 237 and 238 represent adifferential output for output 211 in FIG. 2 b.

Furthermore, the physical layer 208 also includes rectifier circuits 225and 226, and PMOSFETs 231 and 232. The rectifier circuit 225 includes aresistor 227 and a native device 228. The input of the rectifier circuit225 is connected to the input terminal 221 via filter pin 223, andoutput is connected to the gate of the output native device 235 throughPMOSFET 231. Likewise, the input of the rectifier circuit 226 isconnected to the input terminal 222 via filter pin 224, and the outputis connected to the gate of the output native device 236 through PFET232. As will be discussed further herein, the rectifier circuits 225 and226 rectify the input 201 and apply the rectified signal to the gateterminals of the native devices 235, and 236, so as to further turn-onthe relay 210 during the discovery mode. PFETs 231 and 232 are biased toconduct during the discovery mode, so as to apply the rectified outputsfrom the rectifiers 225 and 226 to the gates of the respective outputnative devices 235 and 236. However, the PFETs 231 and 232 are biased tobe cutoff during normal operation mode, so as to prevent the rectifiedoutputs from the rectifiers 225 and 226 from reaching the gates of therespective output native devices 235 and 236. Additionally, the outputnative devices 235 and 236 are biased such that in normal operationmode, the gate-to-source voltage, Vgs, is a negative voltage. Thisensures that the native devices are turned off. This is done bygrounding the gate of the native devices and holding drain and source atthe supply voltage.

In the discovery mode, when no power is applied to the physical layer208, the relay 210 passes through signals 201 to allow for signaldetection by the network 110. However, in the normal operation mode,when the physical layer 208 is powered up, the relay 210 does not allowpassage of signals through to the network 110. Furthermore, the relay210 serves to prevent any possible “leakage” of signals through therelay and minimize the return loss during the normal operation mode. Therelay 210 is constructed using native devices, which are capable ofoperating without any power applied to them. This allows for betterconductivity of the relay and faster detection of the signal by thenetwork 110 during the discovery mode. In the normal operation mode, thenative devices are grounded using additional semiconductor devices.These additional devices operate with application of voltage to them,while the sources and drains of the native devices are held at thesupply voltage. The details of the relay schematic and itsimplementation in the discovery and the normal operation modes arediscussed below.

Discovery Mode

In the discovery mode, (as described by FIG. 2 d), the physical layer208 functions without any power applied to it. The relay 210 is closedin order to facilitate detection of a filtered signal 215 by the network110. More specifically, the output native device 235 and 236 are closed.The differential signal received at the input terminals 221 and 222(similar to receive input 202 of FIG. 2 a) is filtered through theconstant impedance filter 204 and passed through the relay 210. Theoutput of the relay 210 is transmitted out through transmit outputterminals 237 and 238 (similar to the output terminal 213 of FIG. 2 a)and is detected by the network 110. In the discovery mode, the relay 210is capable of rectifying the filtered signal 215 thereby increasing avoltage on the native devices, which it employs, and increasing generalconductivity of the relay 210.

As previously mentioned, the relay 210 uses native devices. The nativedevice, NMOSFET or NMOS (n-channel metal oxide semiconductor fieldeffect transistor), is a device that has a quality of being conductivewhen no bias voltage is applied. In other words, the threshold voltage,Vthresh, is equal to zero. In one embodiment, the threshold voltage ofthe native device is approximately from <100 mV to +100 mV. Whereas,conventional relays employ regular MOSFET devices. Conventional MOSFETdevices require a bias voltage to put them in the conductive state,i.e., a standard depletion voltage of about 400 mV is needed. The use ofnative devices creates a better relay that is capable of being closedduring the discovery mode. In other words, no voltage is required toclose the relay, and the relay is open during the normal operation modeby application of a voltage to the physical layer.

The physical layer 208 includes rectifier circuits that rectify theinput signal 207, and apply the rectified voltage to the gate of theoutput native devices 235 and 236. Referring to FIG. 2 b, two rectifiercircuits 225 and 226 are shown connected to the filter pins 223 and 224,respectively. The filtered signal 215 is passed through the rectifiercircuits 225 and 226, where it is rectified. The rectifier circuit 225consists of a native device 228 and a resistor 227. The rectifiercircuit 226 consists of a native device 230 and a resistor 229. Therectifier circuits 225 and 226 are connected to a pair of output nativedevices 235 and 236, respectively, as shown in FIG. 2 b.

PFET 231, connected between the rectifier circuit 225 and the outputnative device 235 is not engaged in the discovery mode, thereby allowingdirect connection between the rectifier circuit 225 and the outputnative device 235. PFET 232, connected between the rectifier circuit 226and the output native device 236 is not engaged in the discovery mode,thereby allowing direct connection between the rectifier circuit 226 andthe output native device 236. Since, the rectifier circuits 225 and 226are using native devices to rectify the filtered signal 215, suchrectification increases amplitude of the signal 201, which increases thevoltage on the gates of the output native devices 235 and 236. Thisincreases the general conductivity of the relay and faster detection ofsignal by the output terminals 237 and 238. This provides for fasterdetection of the signal at the output terminals 237 and 238 and, hence,the network 110. Such detection of the signal by the network 110 alertsthe network of the presence of the compatible IP telephone system 200,placing the entire system into the normal operation mode.

The relay 210 is shown in more detail in FIG. 5 a. The embodiment shownin FIG. 5 a is one of the four embodiments that the relay 210 may take(others are shown in FIGS. 5 b-5 e and will be described later). FIG. 5a, as well as FIGS. 5 b-5 e, show a portion 590 of the physical layer208. In this embodiment, the relay 210 has positive and negative inputterminals 233 and 234 as well as positive and negative output terminals237 and 238, respectively (as also shown in FIG. 2 b). The positiveterminal 233 is connected to the rectifier circuit 225 and the negativeterminal 234 is connected to the rectifier circuit 226. Each of therectifier circuits are described above in reference to FIG. 2 b. Therectifier circuits 225 and 226 are connected to the output nativedevices 235 and 236 having a common gate connection 510. As statedabove, the PMOS devices 231 and 232, which are active in the normaloperation mode, are not engaged in the discovery mode. These devices 231and 232 serve to ground the gates of native devices 230 and 228 duringthe normal operation mode. Furthermore, another series of gate groundingdevices 262, 263 and 264 are added. These devices are conventionallyknown NMOS devices and are also employed during the normal operationmode. These devices serve to ground the common gate connection 510.

Referring to FIG. 5 a, the filtered signal 215 is received at the inputterminals 233 and 234. The rectifier circuits 225 and 226 rectify thesignal 215 and increase its amplitude. The PFETs 231 and 232 are biasedclosed during discovery mode. Therefore, the output of 226 and 227 areapplied to 510, which increases the voltage at the common gateconnection 510. This, in turn, increases gate voltage on the outputnative devices 235 and 236 making these native devices more conductive,which increases conductivity of the entire relay 210.

The embodiment depicted in FIG. 5 a does not account for a possibledelay in transmission of a signal from the filter during the discoverymode. Referring to FIG. 5 b, another embodiment of the relay is shown.This embodiment of the relay 210 accounts for a possible delay of signaltransmission within the filter. Here, the relay 210 is shown to haveinput terminals 530 directly connected to output native devices 535(similar to output native devices 235 and 236 of FIG. 2 b) and outputterminal pads 540. The relay 210 rectifier circuits 520 (similar torectifier circuits 225 and 226 in FIG. 2 b) are directly attached to thefilter pins 541, which in turn are connected to the constant impedancefilter 204 (not shown). Each rectifier circuit 520 comprises a resistor521 and a native device 522, as shown in FIG. 5 b. The rectifiercircuits 520 are further connected to PMOS devices 524, which serve toground the gates of native devices 522 during the normal operation mode(similar to devices 231 and 232 in FIG. 2 b). These devices (as well asgate grounding devices 536 with respect to the gates of the nativedevices 535) do not ground the gates of native devices 522 during thediscovery mode, since no power is applied to turn the devices 524 on.The devices 524 and 536 and their functions will be described later inconnection to the normal operation mode.

With respect to FIG. 5 b, an incoming signal would come directly to therectifier device 522 and PMOS device 524, bypassing the filter off-chip.This reduces or eliminates any signal delay caused by the rectifiers. Bythe time the signal passes through the filter 204 and comes through theinput 530 and reaches the output native devices 535, the rectifier 522and PMOS device 524 have already conditioned the signal and have turnedon the native devices 535 by applying the rectified signal at the gateof the native device 535. Subsequently, the voltage on the gates of thenative devices 535 is increased, making these devices more conductive,thus, increasing conductivity of the entire relay 210.

FIG. 5 e illustrates another embodiment of the relay portion 590, wherePFET 231 and PFET 232 are cross-connected. More specifically, the gateof the PFET 231 is connected to the drain of the PFET 232 at node 572.Furthermore, the gate of the PFET 232 is connected to the drain of thePFET 231 at a node 571. This connection improves the operation of therectifier circuits 226 and 225 during discovery mode. Since the inputsignal 215 is differential, one of the terminals 233 and 234 receives apositive voltage and the other terminal receives a negative voltage atany give time. By cross-connecting the PFETs 231 and 232, the VGS of atleast one these PFETs will be positive at any given time, regardless ofthe current polarity of the input signal 215. Therefore, the PFETs 231and 232 will turn on faster and stronger during the discovery mode thanwithout the cross-connection.

Normal Operation Mode

After the signal is detected by the network 110 in the discovery mode,the IP telephone system 200 is placed in the normal operation mode,where a voltage source (typically on the order of 3V) is applied to thephysical layer 208, including the input terminals 233, 234 and outputterminals 237, 238. In the normal operation mode, the physical layer 208is powered up, thereby opening the relay 210 and closing switch 205.Since, the filter 204 remains connected to the IP telephone system 200during the normal operation mode, it is desirable to prevent any leakageof signals through the relay 210 to the transmit output 211 (FIGS. 2 aand 2 e). Therefore, the relay 210 is constructed as to not allow anysignals pass through it to the network 110 during the normal operationmode (FIG. 2 a).

In the normal operation mode (as described by FIG. 2 e), an incomingsignal 201 is terminated in a termination resistor 206 after beingpassed through the constant impedance filter 204, as shown in FIG. 2 b.In the normal operation mode, the native devices 228 and 230 and outputnative devices 235 and 236 are grounded. Therefore, no signal passesthrough to the output terminals 237 and 238. The PMOS devices 231 and232, which are turned off by application of voltage, cutoff therectifier outputs of the rectifier circuits 225 and 226. The PMOSdevices 231 and 232 serve to minimize a “leakage” of rectified signalsthrough to the output native devices 235 and 236 during the normaloperation mode. Because the gates of output native devices 235 and 236are grounded and the sources and drains are held at supply voltage, nosignal is able to pass through the relay 210, thereby opening relay 210during the normal operation mode. Moreover, the series of gate groundingdevices 262, 263, and 264 ground the gates of the output native devices235 and 236.

Referring to FIGS. 2 b and 5 a, the gate grounding devices 262-264 areattached to power sources (an analog digital voltage source 261 and ananalog digital ground 207) of the physical layer 208. Referring to FIG.5 a, during the normal operation mode, a voltage source is applied toterminals 261 to turn the gate grounding devices 262-264 on. This, inturn, grounds the gate connection 510 by shorting gate 510 to ground207, thereby grounding the gates of the output native devices 235 and236. Native devices 235 and 236 are cutoff by grounding of theirrespective gates. The gate grounding devices 262-264 are typically NMOSdevices, however, other semiconductor devices may be substitutedinstead, depending on the particular requirements of a circuit.

Furthermore, referring to FIG. 5 a, the PMOS devices 231 and 232 (whichare attached to the native devices 228 and 230 in the rectifier circuits225 and 226, respectively) are attached to the analog digital voltagesource 261 of the physical layer 208. Therefore, in the normal operationmode, the devices 231 and 232 are raised to the level of potentialapplied to the physical layer 208, thus, cutting off the rectifiercircuits 225 and 226 from the output native devices 235 and 236.

Since, the gates of native devices 228 and 230 and the output nativedevices 235 and 236 are grounded, and their respective sources anddrains are held at supply voltage, no signal is capable of passingthrough the relay 210 (as was also described in reference to FIG. 2 b).Any signal that passes through the constant impedance filter 204 isterminated in the termination resistor 206, as shown in FIG. 2 b. In theIP phone 200, the only termination resistor outside the physical layer208 is a resistor 212 connected between the transmitting output 213 andthe physical layer output terminal 211. There is no termination resistorthat is connected between the input terminal 202 and the receiving input203. Therefore, the amplitude of the signal 201 is not reduced duringdiscovery mode since the signal is not terminated prior to the filter204. Furthermore, the on-chip termination 206 only becomes effectiveafter power is applied during the normal operation mode. This can bereferred to as a dynamic termination, since the on chip terminationoccurs only when the power is applied and the switch 205 is closed.Referring to FIG. 2 b, the on-chip termination resistor 206 is shown inmore detail. The structure consists of a pair of resistors 271 and 272and a PMOS device 273 connected to an analog digital ground 207 of thephysical layer 208.

With respect to the embodiment depicted in FIG. 5 b, the relay 210operates similarly in the normal operation mode as its embodimentdescribed in FIG. 5 a. The relay 210 has PMOS devices 524 (similar todevices 231 and 232 of FIG. 2 b) connected to the analog digital voltagesource 261 of the physical layer 208. The PMOS devices 524 ground thegates of the native devices 522 during the normal operation mode.Furthermore, to ensure non-conductivity of the relay the gate groundingdevices 536 (which are connected to the digital analog voltage source261 and the digital analog ground 207) ground a gate connection 539,thereby grounding output native devices 535 (similar to the gategrounding devices 262-264 with respect to the output native devices 235and 236 in FIG. 2 b).

The embodiments of the relay 210 shown in FIGS. 5 c and 5 d are similarin circuit architecture to the embodiments shown in FIGS. 5 a and 5 b,respectively. These embodiments should be considered together withrespect to FIG. 2 c (similar to the schematic shown in FIG. 2 b). Incase of the embodiment shown in FIG. 5 c, the relay's PMOS devices 231and 232 have additional connections 281 and 282, where connection 281 isa connection between the source of the native device 228 and the PMOSdevice 231 (similarly connection 282 is a connection of the source of230 and the PMOS device 232). This embodiment, as well as embodimentshown in FIG. 5 d, allows for lower return loss of the relay 210 duringthe normal operation mode. Similar source connections are made, as isshown in FIG. 5 d, where the source of the native device 522 isconnected to the PMOS 524 at connection 551.

There are other embodiments of the relay are possible, however, theseare some of the embodiments and not to be construed as limiting thescope of the invention, except by the following claims.

Constant Impedance Filter

Filters are commonly used to prevent unwanted frequencies from passingto communication devices. For example, a conventionally known low passfilter consists of an inductor connected in series with a resistor.Referring to FIG. 3 a, a low pass filter 301 (an RL filter) is shown tohave an inductor 302 connected to a resistor 303, which is grounded. Oneproblem with the lowpass filter 301 is that the input impedance of thefilter 301 is a function of frequency, as illustrated by the equations(1) and (2) below:Z=R+sL  (1)|Z|=√{square root over (R ²+(ωL)²)}  (2)wherein Z is the input impedance of the filter; R is resistance of theresistor 303; ω is angular frequency; and ωL is inductive reactance ofthe inductor 302. As shown by equations (1) and (2), the input impedanceof the lowpass filter 301 varies with frequency. The variable inputimpedance causes a variable return loss, which can decrease signalperformance if there is a need for constant impedance circuitry.

As illustrated in FIG. 3 b, another low pass filter 310 is shown to havea resistor 311 connected to a capacitor 312 (a single pole). Low passfilter 310 also has impedance that varies with frequency as presented byequations (3) and (4):

$\begin{matrix}{Z = {R + \frac{1}{sC}}} & (3) \\{{Z} = \sqrt{R^{2} + \left( \frac{1}{\omega\; C} \right)^{2}}} & (4)\end{matrix}$wherein C is the capacitance, R is resistance, ω is angular frequency,and

$\frac{1}{\omega\; C}$is capacitive reactance. As with the RL filter, the impedance of filter310 varies with frequency, producing a variable return loss withfrequency.

FIG. 3 c illustrates a low pass and a high pass filter 320 that has aconstant impedance at all frequencies. Filter 320 includes an inductor321 that series connected with a resistor 322. Inductor 321 and resistor322 are further connected in parallel to a capacitor 323 that is seriesconnected with resistor 326. This filter 320 is capable of maintainingthe following relationship for substantially all frequencies:Z=R  (5)wherein Z is the input impedance and is a pure resistance R. Inembodiments, R is the resistance of the resistors 322 and 326, or aparallel combination thereof. The impedance in equation (5) is derivedfrom equations (6) and (7) that are recited below:

$\begin{matrix}{Z = \left\{ {\left( {R + {sL}} \right)^{- 1} + \left( {R + \frac{1}{sC}} \right)^{- 1}} \right\}^{- 1}} & (6) \\{C = \frac{L}{R^{2}}} & (7)\end{matrix}$

The filter 320 is only a one pole solution. A single pole may notprovide enough attenuation and therefore may allow some unwantedfrequencies to pass through the filter.

FIG. 3 d illustrates a lowpass Butterworth filter 330. The filter 330 isa passive LC filter comprising of multiple poles (LC circuit groups). Inone example, the Butterworth filter 330 is a 5-pole filter, wherein apole includes an inductor 335 and a capacitor 336. The filterattenuation outside the passband of the filter 330 increases with thenumber of poles in the filter 330. However, as the number of poles inthe Butterworth filter 330 increases, the filter response becomes moresensitive to component variations.

The impedance of the Butterworth filter 330 varies with frequency.Within the filter passband, the impedance of the filter is matched andthe signals pass through. However, outside the passband, the impedanceis high and the filter becomes totally reflective. A Butterworth filtercan be configured in a low pass, high pass, and a band pass variety.

FIGS. 4 a-4 e describe a constant impedance filter having multiple polesaccording to the present invention. A constant impedance filtermaintains a constant input impedance through the filter for frequenciesthat are both inside and outside the filter passband. In other words,frequencies inside and outside the filter passband see a substantiallymatched impedance. Frequencies that are inside the filter passband arepassed to the filter output. Frequencies that are outside the filterpassband are terminated inside the filter, and are not reflected.

FIG. 4 a illustrates the function of a filter 204 according to thepresent invention. The filter 204 receives an input signal 202 havingmultiple frequency components. The filter 204 terminates unwantedfrequencies 492 from the input signal 202 into a matched impedance 412,and passes the desired frequencies 211 to the filter output 212. Theinput impedance for the filter 204 is constant for substantially allfrequencies, including those frequencies that are outside the filterpassband. In other words, the input impedance of the filter 204 appearsto be completely resistive.

FIG. 4 b illustrates a constant impedance lowpass filter 204 accordingto embodiments of the present invention. The filter 204 includes aplurality RLC circuit units or poles 410 a, 410 b, 410 c, etc., that areconnected in series with each other. Each RLC circuit unit 410 includesan inductor 405, a capacitor 406, and a resistor 407 and a ground 408,along with a plurality of other poles 410 ending with the terminationresistor 206 and the PMOS relay device 273 (as described in FIG. 2 b).For instance, a pole 410 a will include an inductor 405 a, a capacitor406 a, a resistor 407 a, a ground 408 a, and the plurality of poles 410(such as 410 b, 410 c, etc.) along with the termination resistor 206 andthe PMOS device 273. The input signals come through the input terminals401 and are filtered through the chain of the RLC circuits 410, to anoutput 402. The termination resistor 206 is connected between the PMOSrelay device 273 (which is connected to the output 402) and the ground207.

The filter poles 410 in the filter 204 provide a constant inputimpedance regardless of frequency, if equations (5)-(7) is satisfied.More specifically, the input impedance of each pole 410 is equal to theresistance of the respective resistor 407, as long as the capacitance406 and inductor 405 are chosen according to the relationship inEquation 7. As a result, the filter 204 appears as a pure resistor tothe incoming signal. Frequencies that are outside the passband of thefilter 204 are terminated in a matched impedance, and are not reflected.Frequencies that are inside the passband of the filter 204 are passed tothe output 402.

The angular frequency cutoff of each pole may be determined by thefollowing relationship:ω=R/L  (8)where, ω=2πf.

Each pole 410 can have the same frequency cutoff or each pole 410 canhave a different cutoff frequency, depending on the specification ofdevices connected to the filter. If different cutoff frequencies areselected, then the effect of each pole 410 is cascaded over another pole410. Nonetheless, the filter 204 would appear as a constant impedancefilter across all frequencies as long the equations (5)-(7) aresatisfied.

For a desired cutoff frequency and input impedance (which determines R),the values for L and C for each pole 410 can be calculated by solvingequations 7 and 8. For example, if the desired input impedance is 100ohm and the desired cutoff frequency is 2.274 MHz for a pole 410, then Lis found using equation 8 and C is found using equation 7, where L is7.0 uH and C is 700 pF.

As stated above, the cutoff frequencies of each pole 410 can be selectedto be same, or the cutoff frequencies can be different in for each pole410 in the filter 204. Additionally, the resistors 407 can be identicalfor each pole 410 in the filter 204, or the resistors 407 can vary fromone pole 410 to another pole 410. If the resistors vary from pole topole, then input impedance at 401 is the based combination of theresistors 407 in each pole 410 and the termination resistor 206,assuming that equations (5)-(7) are satisfied in each pole.

In one embodiment, the resistor 407 is the same for each pole 410 and isequal to the termination resistor 206. In this embodiment, the inputimpedance at the terminal 401 is the resistance of the resistor 407,assuming equations (5)-(7) are satisfied.

Referring to FIG. 2 b, the termination resistor 206 is configured usingresistors 271 and 272 and a PMOS relay device 273 that is connected toground terminal 207. The resistors 271 and 272 are connected across theterminals 233 and 234 when the PMOS relay 273 is closed. The resistors271 and 272 provide a termination for the filter 204 when applied acrossthe terminals 233 and 234. During discovery mode, no voltage is appliedto the physical layer 208, so the terminal 207 is allowed to float openand the resistors 271 and 272 are not applied across the terminals 233and 234. Therefore, the filter 204 is not terminated during thediscovery mode, as represented by the open relay 205 in FIG. 2 d. In thenormal operation mode, a ground voltage is applied at terminal 207 tothe gate of the PMOS device 273, causing the PMOS device to conduct andapply the resistors 271 and 273 across the terminals 233 and 234.Therefore, the filter 204 is properly terminated during the normaloperation mode, produce the desired constant impedance across allfrequencies. Furthermore, in the normal operation mode, any signal thatcomes through the filter is terminated in the resistors 271 and 272since the PMOS device 273 is closed and the relay 210 is open. Thesignal is analogously terminated in the following embodiments of thefilter 204.

FIG. 4 c illustrates a bandpass filter 204 that has a constant inputimpedance. Referring to FIG. 4 c, the input signals come in through aninput terminal 401 encountering a series of RLC circuit units or poles420 (a, b, c, etc.). Each pole 420 includes an inductor 423, a capacitor424, and a resistor 425 and a ground 426, along with a plurality ofother poles 420 ending with a termination resistor 206. For instance, apole 420 a will include an inductor 423 a, a capacitor 424 a, a resistor425 a, a ground 426 a, along with a plurality of poles 420 (such as 420b, 420 c, etc.) that end with the termination resistor 206 and the PMOSrelay device 273. The chain of RLC poles 420 ends with the terminationresistor 206, the PMOS relay device 273 and the ground 207. In the pole420 c, the resistor (not shown) is removed leaving only the capacitor424 c (as shown). A chain of highpass circuits or poles 430 (a, b, c,etc.) are attached to one terminal of the capacitor 424 c, so as to bein parallel with the lowpass poles 420. Therefore, the lowpass poles 420a, 420 b, and 420 c includes a plurality of lowpass poles 420 and theplurality of highpass poles 430 along with respective terminationresistors 206 and the PMOS relay devices 273. Subsequent lowpass poles420 (i.e., 420 d, 420 e, etc.) include only the plurality of lowpasspoles 420 and not the plurality of highpass poles 430. It is clear, thatthe plurality of highpass poles may be attached to the plurality oflowpass poles at any given lowpass pole 420. Each highpass pole 430includes an inductor 432, a capacitor 431, and a resistor 433 and aground 434 along with a plurality of other poles 430 ending with thetermination resistor 206 and the PMOS relay device 273. For instance, apole 430 a will include an inductor 432 a, a capacitor 431 a, a resistor433 a, a ground 434 a, and the plurality of poles 430 (such as 430 b,430 c, etc.) along with the termination resistor 206 and the PMOS device273. The filter 204, shown in FIG. 4 c, has a bandpass responsedetermined by the lowpass cutoff frequency of the poles 420, and by thehighpass cutoff frequency of the poles 430. The cutoff frequency of thelowpass poles 420 and the highpass poles 430 are determined by theequation 8. As in FIG. 4 b, the inductor and capacitors in the lowpasspoles 420 and the highpass poles 430 can be selected to provide aconstant input impedance for each pole 420, 430 by satisfying Equation(5)-(7). If the lowpass poles 420 and the highpass poles 430 areselected to have the same constant input impedance, then the inputimpedance of the at the terminal 401 will have the selected inputimpedance.

FIG. 4 d shows a differential lowpass filter 204 that has a constantimpedance according to embodiments of the present invention. The filter204 includes a plurality RLC circuit units or poles 440 a, 440 b, 440 c,etc., that are connected in series with each other between an input 401and an output 402. Each pole 440 includes a first inductor 443, a secondinductor 446, a capacitor 444, a resistor 445, along with other poles440 that end in the termination resistor 206 and the PMOS relay device273. The input signals come through input terminals 401 a and 401 b,wherein terminal 401 a can serve as an input means for a positivedifferential component and input terminal 401 b may serve as an inputmeans for a negative differential potential. The output of the filter204 is taken across output terminals 402 a and 402 b. The terminationresistor 206 and the PMOS relay device are connected across the outputterminals 402. As with the filters 204 shown in FIGS. 4 b and 4 c, eachpole 440 maintains a constant impedance to an incoming signal, if theinductors 443, 446 and the capacitor 444 satisfy equations (5)-(7). Whenusing equations 7 and 8, the calculated inductor values are divided by2, and assigned to the inductors 443 and 446. For example, if theinductor value is calculated to be 7.0 uH from equations 7 and 8, thenthe inductors 443 are set to 3.5 uH and the inductors 446 are set to 3.5uH.

Filter 204 is illustrated to have 3 poles. However, any number of filterpoles could be utilized. For example, filter 204 in FIG. 4 e has fourRLC poles 440 (a, b, c, d) connected in series between the input 401 andthe output 402. Each pole 440 includes the first inductor 443, thesecond inductor 446, the capacitor 444, the resistor 445, along withother poles 440 that end in a termination resistor 206 and the PMOSrelay device 273. Filter 204 of FIG. 4 e is also a differential filteras is the one shown in FIG. 4 d. An input differential signal comes inthrough terminals 401 a and 401 b and passes through each individualpole 440 (a, b, c, d). The incoming signal after being filtered througheach individual pole, is terminated in the termination resistor 206.

The values of each of the resistors 445 in both FIGS. 4 d and 4 e maydiffer as well as the values of inductors 443 and 446 and capacitors444. However, the filters 204 of FIGS. 4 d and 4 e will have a constantinput impedance as long as the relationship described by formula (7) issubstantially maintained within each individual pole. Each pole in allof the embodiments of the present invention filter is independent ofanother pole, which makes the filter more advantageous over conventionalfilters. It is understood by one skilled in the art that the presentinvention is not limited to the embodiments shown in FIGS. 4 a-4 e, asother arrangements will be apparent to those skilled in the art based onthe discussion given above. In embodiments of the invention, the filtersdescribed herein have at least two poles in order to avoid sensitivityof components in the filter.

The differential filters shown in FIGS. 4 d and 4 e have a better noisereduction parameters than single-ended filters, shown in FIG. 4 b and 4c. The values of the elements comprising the poles 440 do not need to bethe same, i.e., resistor in one pole does not need to be equal to theresistor in another pole. Nonetheless, as long as the relationship inequation (7) is preserved, each pole is independently preservingconstant impedance through the entire chain of the poles.

The constant impedance of the present invention filter allows the filterto be connected to other circuitry at all times, without regard forunwanted signal reflections. For example, the present invention filtercan be connected to the physical layer of an IP telephone system at alltimes. This is an advantage over the conventional filter, which utilizesoff-chip relays to connect/disconnect the conventional filter to/fromthe physical layer, depending on the mode of operation. Since thepresent invention filter is connected at all times, this alleviates theconnecting/disconnecting of the filter when the system changes itsmodes.

In one embodiment of the present invention, the values of the componentsof the filters 204 of FIGS. 4 d and 4 e may be as follows. The resistors445 are of 100 ohm each. The capacitors 444 are of 700 pF each. Theinductors 443 and 446 are of 3.5 u each. The mentioned vales willproduce a constant input impedance of approximately 100 ohms at theinput of the filters 204 of FIGS. 4 d and 4 e, according to equation(7). These values are provide for example purposes only, and are notmeant to be limiting. Other filter component values will apparent tothose skilled in the arts based on the discussion given herein.

Since, the filter poles are independent of one another, one canconstruct the filters according to a band of frequencies supplied to it.For example, if it is desired to have a filter accepting only 1 MHzfrequencies, then all poles would have a 1 MHz passband response. If itis desired that the filter would have a gradual response to a range of 1MHz to 10 MHz, each pole may have a different passband responseaccording to the range.

FIG. 6 illustrates a communications system 600 having a switch 602 thatis coupled to a DTE 610 over a LAN 606, wherein power 604 is applied toover the LAN 606 to the DTE device 610 using a DC-DC converter 608. TheDTE device 610 is preferable an IP phone, wireless access point, orother device that can be properly powered by the power supply 604.Legacy devices cannot be powered by the power supply 604 and thereforeshould be shielded from being powered by the power supply 604. Forexample, legacy network interface cards (NICs) can be permanentlydamaged if the power 604 is applied over the LAN 606. Further, legacydevices may also cause a fire hazard if improperly connected to a powersupply. Accordingly, it is highly desirable to determine if the DTE is aconforming network device (i.e. non-legacy device) prior to applyingpower to over the LAN. Herein the term “conforming network device” for aDTE includes, for example, an IP Phone that is configured to be poweredover a LAN. However, “conforming network devices” are not limited to IPphones, but also include other devices that are intended to be poweredover a LAN, such as wireless access points, small switches, and otherdevices etc. A particular DTE is determined to be a conforming device orlegacy network (i.e. communications) device during the discovery mode.

FIG. 7 illustrates a communications system 700 that is similar to thecommunications system 600, but includes a filter 702 that is intended toprevent legacy devices from being interpreted as IP phones by the switch602 during discovery mode. The switch 602 transmits normal link pulses701 for legacy devices, but transmits extended link pulses 704 for IPphones. For example, the normal link pulses 701 could be 10Base-T or100TX pulses, and the normal link pulses 701 are higher frequency thanthe extended link pulses 704. The lowpass filter 702 is configured toblock normal link pulses 701 but passes extended link pulses 704 so thatthey are returned to the switch device 602, indicating the presence ofan IP phone at the DTE 610. This occurs because the frequency spectrumof the normal link pulses 701 is higher than that of the extended linkpulses 704, and the cutoff frequency of the lowpass filter 702 isconfigured to reject the normal link pulses but pass the extended linkpulses. The communications system 700 requires four relays because thefilter 702 is coupled across the transmit and receive ports of the DTE610 for discovery mode. However, once discovery mode is concluded, thefour relays are opened so that that the filter is disconnected fornormal operation to begin. During normal operation, the TX and REC portsof the DTE are operational. As discussed above, the filter relays canoften wear over time, increasing repair costs. Additionally, the filteris an external device which increases assembly time and costs.

FIG. 8A illustrates a communications system 800 that is similar to thecommunications system 700, but the lowpass filter 802 is connected allthe time and is connected to a filter node of the DTE 602. The lowpassfilter 802 is configured to block normal link pulses 701 but passextended link pulses 704 so that they are returned to the switch device602, indicating the presence of an IP phone at the DTE 610 duringdiscovery mode. The relay in DTE 610 is open during normal modeoperations, similar to the discussion of FIGS. 2A-2D. In other words,the communications system 800 represents the IP phone discussed in FIGS.2A-2D, where the rely 210 is closed and the switch 205 is open duringdiscovery mode.

A problem can occur with the communications system 800 if the low passfilter 802 does not sufficiently attenuate the normal link pulses 701.This can occur for example when switch 602 is a legacy switch that issending normal link pulses over a short cable and the pulses are notsufficiently attenuated by the low pass filter 802. In which case, theswitch 602 may receive normal link pulses 701 that are inadvertentlypassed by the IP phone, causing the switch 602 to interpret the IP phoneas a legacy device instead of a non-legacy device. In other words, thedevices can link up. If the legacy switch then transmits data packetsover the LAN, then these data packets can also pass through the filter702, creating an unintended and unauthorized signal loop that violatesIEEE standards.

FIG. 8B further illustrates the normal or fast link pulses 701, whichare 100 ns wide pulses with a period of 16 mS. Extended link pulses thatare associated with IP phones are larger, but are much less continuousthan the normal link pulses. For example, extended link pulses can bebetween 150 nS wide to 1000 nS wide, but with a much lower period thanthe normal link pulses. Further, FIG. 8C illustrates data packets 802for comparison, which are a much longer duration signal than both normallink pulses and extended link pulses. For example, but withoutlimitation, data packets can be 1-3 microseconds long. Accordingly, datapackets put much more energy on the LAN cable than either extended linkpulses or normal link pulses because the signal is active for a longerperiod of time. Herein, data packets can be described as a “highduration signal”, a “high time duration signal”, a “long durationsignal”, a “long time duration signal” to describe the distinctionrelative extended link pulses and normal link pulses. The data packetscan also be described as having a signal profile that has a “longeractive period” than that of the extended link pulses and the normal linkpulses because the data transmission last 1-3 microseconds. As such, theactive signal period is one or two orders of magnitude higher than thatof the normal link pulses and the extended link pulses.

FIG. 9 further illustrates the communications system 800 duringdiscovery mode. FIG. 9 includes a physical layer 902 of the DTE device610 in the communications system 800. The physical layer 902 includesfilter pins 904 and 906 that are coupled to the low pass filters 802.Low pass filters 802 are intended to block normal link pulses 701 anddata packets 802, and pass the extended link pulses 704. The filter pin904 receives the filtered output from the low pass filter 802 a. A relay907 is between the filter pins 904 and 906. The relay 907 is closedduring discovery mode to allow passage of the extended link pulses 704,but opened during normal mode. The lowpass filter 802 b further filtersthe output of the relay 907.

FIG. 10 illustrates the relays 907 being implemented with native FETdevices 1002 that are naturally on, unless turned off via a negativevoltage on the gate terminals 1004 a and 1004 b. Further, the FETdevices 1006 are turned on during discovery mode, and provide anadditional bias boost to the native FET devices 1002, to further reducetheir on resistance.

FIG. 11 illustrates a physical layer device 1100 that addresses theconcerns regarding short cable lengths discussed with reference to thecommunications systems 800 and the physical layer device 900. Morespecifically, the physical layer device 1100 prevents data packets 804from being transmitted back to the switch 602, even when the LAN cablelength is short.

Still referring to FIG. 11, the physical layer device 1100 includesnative devices 1002 to provide the relay between the filter pins 904 and906, as in FIG. 10. The physical layer device 1100 further includes arectifier 1102 and a lowpass filter 1104 that are series coupled to thegate of an N-FET 1106. In an embodiment, the cutoff frequency of thelowpass filter 1104 is approximately 250 kHz. The source of the N-FET1106 is coupled to ground and the drain is coupled to the gates of thenative FETs 1002 as shown.

The physical layer device 1100 operates to shut-off the native devicesfor input signals that are highly continuous in nature, such as datapackets. Stated another way, the physical layer device 1100 isconfigured to shut-off the native devices for input signals that have arelatively high signal duration. As discussed above, data packets arehighly continuous relative extended link pulses, as they have signaldurations that can last from 1-3 microseconds. However, the inventiondescribed herein is not limited to the mentioned signal periods for datapackets, as the circuit elements can be tuned for other signal timeperiods, as will be understood by those skilled in arts.

During operation, the data packets 804 are received by the filter pins904. The rectifier 1102 rectifies the data packets 804 to generate arectified signal having an increasing amplitude over time. The rectifiedsignal has a substantially low frequency (or even DC) and passes throughthe low pass filter 1104. The data packets 805 have a sufficiently highsignal duration and are sufficiently continuous, that the rectifiedsignal will increase to an amplitude sufficient to cause the N-FET 1106to conduct, which grounds the gates of the native FETs 1002. In otherwords, the data packet signal duration of 1-3 microseconds is sufficientto generate a rectified signal large enough to cause the NFET 1106 toconduct and cut-off the native devices 1002. Accordingly, the datapackets 804 will cause the native FETs 1002 to cut-off, preventing thedata packets 804 from reaching the filter pins 906. Therefore, the datapackets 804 are not re-transmitted to the switch 602, preventing anun-authorized loop transmission back to the switch. As such, there thephysical layer device 1100 prevents IEEE violations for unauthorizedloop transmission from IP phones that receive packets from legacydevices.

However, the extended link pulses 704 have a low signal duration whencompared to that of the data packets 804, so that the rectifier 1102cannot generate a rectified voltage that is sufficiently large toturn-on the N-FET 1106. In other words, the extended link pulses 704 aremore sporatic than the data packets 804. Accordingly, the N-FET 1106does not conduct for the extended link pulses 704, so that the nativedevices 1002 remain conducting for the extended link pulses 704. It isreminded that the native devices 1002 are normally “on” with 0 volts orno voltage on their gates. Accordingly, the extended link pulses areproperly re-transmitted to the switch device 602, indicating acompatible IP phone or other conforming device at the DTE 610.

In summary, the rectifier 1102 and filter 1104 combination analyze theincoming pulses and produce a control voltage that grounds the gates ofthe native devices 1002 in the relay so as to cut-off the relay, butonly for the more continuous data packets.

Devices 1108 further rectify the extended link pulses 704 received atthe filter pins 904 so as to improve the conductivity of the nativedevices 1002 when receiving extended link pulses.

CONCLUSION

Example embodiments of the methods, circuits, and components of thepresent invention have been described herein. As noted elsewhere, theseexample embodiments have been described for illustrative purposes only,and are not limiting. Other embodiments are possible and are covered bythe invention. Such embodiments will be apparent to persons skilled inthe relevant art(s) based on the teachings contained herein. Thus, thebreadth and scope of the present invention should not be limited by anyof the above-described exemplary embodiments, but should be defined onlyin accordance with the following claims and their equivalents.

1. A communications device, comprising: a substrate having an input andan output that is capable of being connected to a communicationsnetwork; a relay, disposed on said substrate and connected between saidinput and said output of said substrate, said relay capable of beingclosed when no voltage is applied to said relay, said relay including anative field effect transistor (FET) having a source and a drain, saidinput to said substrate connected to one of said source and said drain,and said output connected to the other of said source and said drain;means for grounding a gate of said native field effect transistorresponsive to a high duration signal received at said substrate input,wherein said high duration signal includes data packets that areassociated with legacy devices.
 2. The communications device of a claim1, wherein said communications device includes one of: an IP phone, awireless access point, a local switch, and wherein said communicationsdevice operates according to a discovery mode during auto-negotiation.3. The communications device of claim 1, wherein said communicationsdevice is responsive to extended link pulses during a discovery mode,said extended link pulses having an active signal duration that is lowerthan that of said data packets.
 4. The communications device of claim 3,wherein said means for grounding causes said relay to reject said datapackets, and pass said extended link pulses during said discovery mode.5. The communications device of claim 1, wherein said means forgrounding includes: a switch having a first terminal coupled to groundand a second terminal coupled to a control terminal of said native fieldeffect transistor; a rectifier having an input coupled to said input ofsaid substrate; and a low pass filter having an input coupled to anoutput of said rectifier, an output of said low pass filter coupled tosaid gate of said switch; wherein said switch, said rectifier, and saidlow pass filter are all integrated on said substrate.
 6. Thecommunications device of claim 5, wherein said rectifier rectifies saidhigh duration signal to generate a rectified signal that closes saidswitch, thereby grounding a gate of said native device and causing saidrelay to reject said high duration signal.
 7. The communications deviceof claim 6, wherein said rectifier does not rectify extended link pulsesduring a discovery mode so that said switch remains open when saidrectifier receives said extended link pulses, thereby causing said relayto remain closed and pass said extended link pulses.
 8. Thecommunications device of claim 7, wherein said low pass filter has acutoff frequency configured so that said switch is unresponsive toextended link pulses.
 9. The communications device of claim 5, whereinsaid cutoff frequency is approximately 250 kHz.
 10. The communicationsdevice of claim 5, further comprising a means for reducing resistance ofsaid native device when receiving extended link pulses.
 11. Thecommunications device of claim 10, wherein said means for reducingincludes a second rectifier having an input coupled to said substrateinput and an output coupled to said gate of said native device.
 12. Thecommunications device of claim 11, wherein said second rectifierrectifies said extended link pulses so as to boost a gate voltage ofsaid native device.
 13. A communications device, comprising: a substratehaving a differential input and a differential output that are capableof being connected to a communications network; a differential relay,disposed on said substrate and connected between said input and saidoutput of said substrate, said differential relay including first andsecond native FETs that are conductive without a voltage on theirrespective gates; a switchable ground coupled to gates of said first andsecond native FET; and a rectifier and filter means that rectifies datapackets to activate said switchable ground, thereby cutting-off saidfirst and second native FETs and opening said differential relay so asto reject said data packets.
 14. The communications device of claim 13,wherein said rectifier and filter means includes: a rectifier and filterseries coupled to said differential input, and an output of said filtercoupled to control said switchable ground.
 15. The communications deviceof claim 13, wherein said rectifier and filter means is unresponsive toextended link pulses received at said differential input, so that saidfirst and second native FETs remain conductive and pass said extendedlink pulses to said differential output.
 16. The communications deviceof claim 15, wherein said extended link pulses are relatively lesscontinuous than said data pulses.
 17. The communications device of claim15, wherein said data packets pulses have a higher active signalduration than said extended link pulses.
 18. The communications deviceof claim 15, wherein said data packets provide auto-negotiation forlegacy devices.
 19. The communications device of claim 15, furthercomprising a second rectifier means for receiving said extended linkpulses and boosting a gate voltage of said first and second nativedevices, so as to improve conductivity of said first and second nativedevices.
 20. A communications device that receives data packets andextended link pulses, said data packets having a higher active signalduration than said extended link pulses, and said data packetsassociated with a legacy device, comprising: a substrate having an inputand an output that are capable of being connected to a communicationsnetwork that transmits said extended link pulses and said data packets;a relay, disposed on said substrate and connected between said input andsaid output of said substrate and having a control terminal, said relayconfigured to be conductive when no voltage is applied to said controlterminal; and means, disposed on said substrate, for producing a controlvoltage that opens said relay upon receiving said data pulses.
 21. Thecommunications device of claim 20, wherein said means for producing istriggered by said higher signal duration of said data packets.
 22. Thecommunications device of claim 20, wherein said communications device isone of an IP phone, a wireless access point, and a local switch.